A. Technical Field
The present invention relates generally to the management of stress on a semiconductor device, and more particularly, to the manufacturing and design of a stress management layer on a semiconductor device.
B. Background of the Invention
Semiconductor devices are sensitive to mechanical stress, which may misshape or otherwise harm a semiconductor device. This mechanical stress may adversely affect the performance of the device, and over time, reduce the length of its operative life. One source of mechanical stress is a package, in which a semiconductor device is located, that functions to protect the semiconductor device from its environment and provides an interface for electrical and potentially optical signals.
A semiconductor device may be packaged in various types of semiconductor packages. Examples of available semiconductor packages include transfer molded and pour molded packages. Typically, these packages are made of a molding compound that surrounds the semiconductor device and functions as a barrier between the device and the outside environment. Although the purpose of this molding compound is to protect the semiconductor device, it may actually harm the device as it reacts to temperature changes. This package molding compound may expand or contract at a different rate than the semiconductor device relative to temperature changes caused either by the semiconductor device itself or the outside environment. In particular, the molding compound and semiconductor device may have different thermal expansion coefficients which cause different rates of expansion or contraction relative to a temperature change. This expansion or contraction of the surrounding molding compound applies mechanical stress on the semiconductor device and may reduce the performance, shorten the life, or otherwise damage the device. Thus, as the semiconductor device goes through a series of temperature cycles, the damage caused by this mechanical stress may be compounded resulting in significant shortening of the operative life of the semiconductor device.
One semiconductor device that is particularly sensitive to outside mechanical stress is a surface emitting laser. Surface emitting laser devices also have specific requirements for packaging that may limit the options available to compensate for this mechanical stress. In particular, the molding compound and any filler material between the compound and the device need to be relatively clear to allow light to be emitted from the device. Plastic packaging, having certain transparent properties, is typically used to package surface emitting laser semiconductor devices. As described above, this plastic packaging may expand and contract at a different rate relative to temperature than does the surface emitting laser semiconductor device. Accordingly, as the package molding and filler material expands or contracts, mechanical stress may be placed on the surface emitting laser semiconductor device or components therein.
Certain components or areas of a semiconductor device are particularly sensitive to mechanical stress. For example, an active region within a surface emitting laser is more easily damaged from stress than other components of the laser. This active region contains components, such as mirrors that create a lasing cavity. External stress may induce mechanical stress into these components and thereby diminish the operation of the lasing cavity and the surface emitting laser. Other semiconductor devices, such as other types of lasers or sensors of several varieties, may also contain specific components that are highly-stress sensitive. As a result, a semiconductor device may have certain areas or components that need more protection against stress than other components in the device.
Current methods to reduce stress on a semiconductor device are often difficult, expensive and time consuming to apply. One such method is the use of a syringe to drop liquid material, on a semiconductor device after fabrication. This method, however, does not allow stress management material to be patterned on a substrate nor provide any control of the thickness of this material on the semiconductor itself. Additionally, these current methods are unable to specifically address certain portions of a semiconductor that may be more sensitive to stress, while leaving uncovered other areas for facilitation of electrical contact, for example.